Excessive alcohol consumption is known to adversely affect health and to greatly increase health care costs. Less is known, however, about the potential impact of light and moderate drinking on the use of health care services and costs. This study examines the relationship between levels of alcohol consumption and health care utilization and costs among primal care patients. The setting is Kaiser Permanente, Northwest Region (KPNW), an HMO serving 375,000 members. For a previous study, approximately 8,000 patients completed a questionnaire that included the AUDIT (an instrument developed by the World Health Organization to identify hazardous drinking levels), a separate measure of quantity and frequency of drinking, smoking status, and sociodemographic characteristics. In addition to the AUDIT, a continuous measure, drinking categories will be defined to include abstainers, former drinkers, and current drinkers (lighter, moderate, heavier). These data will be linked to KPNW administrative and clinical data bases to collect health care utilization data for one year before and one year after the patient's questionnaire date. Utilization data include the number of outpatient visits (for scheduled appointments. urgency' care, and emergency care), number of prescription drug dispensings. number of claims from non-KPNW vendors, and number and length of hospitalizations. Costs will be estimated by weighting the utilization events by appropriately-defined cost coefficients and summing over the two-year observation period. Multiple regression, analysis of covariance, and logistic regression analyses will be used to assess the association between alcohol consumption (including both continuous and categorical measures) and health care utilization indicators, after adjusting for gender, age, race, educational level, marital status, and smoking status. This study will contribute to research on the role of alcohol in creating demand for health care services and will be of interest to health policy planners seeking to understand the impact of drinking on medical care costs in large managed care systems.